Central Taiwan Earthquake Sept. 20, 1999
Special event page for the the Taiwan earthquake at IRIS.
-
Current news on the Taiwan earthquake from Kazuhiko Sato and Jim Mori
of the Disaster Prevention Research Institute, Kyoto University.
- Early strong-motion records in Report #1 and Report #2
compiled by the Central Weather Bureau (CWB) for the Chi-Chi
(Taiwan) earthquake.
-
A brief report on the Taiwan M7.6 earthquake from
Charles P. Watson of Seismo-Watch.
A Report from Koji Okumura, Hiroshima University
According to Asahi newspaper [iij.asahi.com], the victims
of the Taiwan earthquake is more than 1500 and 2500 people
are still missing as of 21:00 JMT [GMT +9:00].
I made a map of historic seismicity in and around
Taiwan in my homepage for your information. The
epicenters are based on catalogues by Utsu (1996, 1998).
Please visit:
http://www.ipc.hiroshima-u.ac.jp/~kojiok/taiwan.gif
According to Ota and Okada (1984 in Japanese) based
on Hsu and Chang (1979), major active faults run
along the western foot of the Central Mountains* and
along the longitudinal valley between Coastal Range
and Central Mountains. Along the western foot, 1906,
1935, 1946 ruptured the surface notwithstanding their
smaller magnitude.
The epicenter of the Sept-21-1999 earthquake is located
in another longitudinal valley running through the Central
Mountains. The valley is obvious from 1 km DEM, but
is not clear on 1/50,000 topo maps in the epicentral
area, maybe owing to severe erosion.
The Sept-21-1999 shock seems to be the largest in
central Taiwan [or in the proximity of densely inhabited
area in western Taiwan], since 1600. The relatively
smaller magnitude of the earthquakes before 1999 is
remarkable.
Koji Okumura
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Koji Okumura, Department of Geography
Hiroshima University, Higashi-Hiroshima, 739-8522, JAPAN
Fax: +81-824-240320, Phone: +81-824-246657
***** http://www.ipc.hiroshima-u.ac.jp/~kojiok/ *****
==========================================================
Focal Mechanisms:
From: Stuart Sipkin
Date: Mon, 20 Sep 1999 15:37:27 -0600 (MDT)
Message-Id: <199909202137.PAA19579@cora.cr.usgs.gov>
Subject: 20SEP99 TAIWAN
99/09/20 17:47:19.01
TAIWAN
Epicenter: 23.781 121.090
mb 6.3 MS 7.6
MOMENT TENSOR SOLUTION
Depth 5 No. of sta: 23
Moment Tensor; Scale 10**20 Nm
Mrr= 1.93 Mtt= 0.01
Mff=-1.94 Mrt=-0.76
Mrf=-1.20 Mtf=-0.33
Principal axes:
T Val= 2.44 Plg=69 Azm=138
N -0.04 11 17
P -2.40 17 283
Best Double Couple:Mo=2.4*10**20
Mw=7.6
NP1:Strike=357 Dip=29 Slip= 67
NP2: 202 63 102
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- ---------#############-----
-- P --------##############------
-- -------################-----
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-----------####### #######-----
----------######## T #######-----
---------######## ######-----
--------##################-----
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---##############----
--###########----
#####--
Date: Tue, 21 Sep 1999 12:52:56 +0900 (JST)
From: autocmt
Message-Id: <199909210352.MAA22939@global.eri.u-tokyo.ac.jp>
To: globalCMT@global.eri.u-tokyo.ac.jp
Subject: ERI automatic CMT inversion
The following is our updated autoCMT solution for the Taiwan event.
The previous autoCMT solution was determined using records from only one station,
and the solution quality was extremely low.
Our most updated solutions (with regional seismicity map)
can be always found at our WEB site
(URL: http://www.eri.u-tokyo.ac.jp/~http/AUTO_CMT/auto_cmt.html).
H. Kawakatsu
------------------------- ERI automatic CMT inversion (combined) --------------
TAIWAN (ms 7.6)
1999-09-20 17:47:19.0 (QED) Mo=2.48**27(dyne-cm) Mw=7.5
lat: 23.80 lon: 121.10 dep: 33.0 (QED)
CMT solution: unit in 1e+27 (dyne-cm) ---------###
lat: 23.72 lon: 121.12 dep: 23.6 (CMT) ----------##########
Mrr: 2.37 +- 0.07 Mrt: 0.35 +- 0.11 -----------###############
Mtt: -0.70 +- 0.03 Mrf: -0.97 +- 0.13 ----------#################--
Mff: -1.67 +- 0.07 Mtf: -0.87 +- 0.04 P ---------###################--
T-axis Val= 2.68 Plg= 72.9 Azm = 56.6 --------####### ##########---
N-axis Val= -0.40 Plg= 14.7 Azm = 205.0 -----------######## T ##########----
P-axis Val= -2.28 Plg= 8.6 Azm = 297.3 ----------######### #########-----
Best Double Couple: Mo=2.48**27 Mw=7.5 ----------####################------
nodal planes (strike/dip/slip): ----------###################-------
44.2/ 38.6/114.0 194.5/ 55.2/ 72.0 ---------##################-------
Half duration: 15.8 --------################--------
NDC: epsilon= 0.15 isotropic= 0.0(%) -------#############----------
Comment: ------########------------
####----------------
Note large non-double couple comp.! #-----------
CMT solutions combined:
bodywave [10,12,20,22mHz] Fit: 26% of 40 records; Azimuth: 8 of 12
Mo ratio: 1.36; MT correlation: 0.90; Centroid: 0.08 degree & -9 km from QED
surface wave [2,2.5,7,7.5mHz] Fit: 99% of 3 records; Azimuth: 1 of 12
Mo ratio: 1.06; MT correlation: 0.71; Centroid: 2.15 degree & -7 km from QED
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